1882.] On the Embryo o/Peripatus Capensis. 



391 



has been considered more expedient that these should at once be 

 communicated to the Royal Society in the present note. 



The Blastopore. — Balfour left no manuscript account or notes of his 

 discovery in connexion with the drawings which he prepared in order 

 to illustrate it, but he spoke about it to Professor Ray Lankester and 

 also to us, and he further gave a short account of the matter in a 

 private letter to Professor Kleinenberg, from which, by the courtesy 

 of that distinguished embryologist, the following extract is made : — 



" There is (in the early embryo of Peripatus capensis) along the whole 

 ventral surface a groove which, leads into the alimentary canal, and, 

 as shown in sections, the walls of the alimentary canal give off pouches 

 like those in Amphioxus, which form the mesoblastic somites. The 

 hypoblast cells are large and filled with yolk, but the alimentary canal 

 has a clear lumen. I have not yet got earlier stages, and the next 

 later stages only differ from that described in the fact that the 

 groove-like blastopore is closed and the mesoblastic somites are more 

 numerous, while two widely separated thickenings of the epiblast 

 constitute the first rudiments of the ventral nerve- cords." 



The drawings left by Balfour in connexion with the above remark- 

 able discoveries are four in number : one of the entire embryo, show- 

 ing the slit-like blastopore and the pouch-like outgrowths of the 

 archenteron, the other three depicting the transverse sections of the 

 same embryo. 



The first drawing, viz., that of the whole embryo, shows an embryo 

 of an oval shape, possessing six somites, whilst along the middle of its 

 ventral surface there are two slit-like openings, lying parallel to the 

 long axis of the body, and placed one behind the other. The meso- 

 blastic outgrowths are arranged bilaterally in pairs, six on either 

 side of these slits. The following note in his handwriting is attached 

 to this drawing : — 



" Young larva of Peripatus capensis. I could not make out for 

 certain which was the anterior end. Length 1'34 millims." 



One of these openings is much longer than the other, and they 

 present the appearance of having been once part of a single continuous 

 slit, running nearly the whole length of the embryo. Balfour's own 

 statement in the above letter, and two other embryos, which we have 

 found among his material, prove that such is the case. These em- 

 bryos, both taken from the uterus of the same female, are of two 

 ages, but both are younger than that from which Balfour's drawing 

 was made. The youngest is "7 millim. in length and possesses three 

 somites and a continuous slit extending along nearly the whole length 

 of its ventral surface. The older one is '86 millim. in length and 

 possesses five somites. In this embryo the side walls of the middle 

 portion of the slit have come together, preparatory to the fusion, 

 which will almost immediately divide it into two parts. These two 



vol. xxxiv. 2 D 



